Optical fibers have been the medium of choice in the field of optical communications for long distance propagation of light due to their excellent transmission characteristics and ability to be fabricated in lengths of many kilometers. Light propagates through the core region of optical fibers that can be as small as a few microns in diameter.
Optical fiber and lens arrays are used to couple light between optical fibers and optical devices in optical communication systems. Conventional optical fiber and lens arrays typically include an array of fibers arranged in a silicon v-groove positioning element, and the fiber ends are abutted to a lens array, which can be molded from an appropriate polymeric material. One limitation of this type of fiber and lens arrays is that since the lenses and fibers are separate elements, it is difficult to optimally align the core region of the optical fiber with the lens, which results in insertion loss.
Lensed optical fibers are devices that include a fiber having a lens formed on the end of the fiber. The assignee of the present invention manufactures lensed fibers under the OptiFocus™ product line, which includes lensed fibers for collimating, focusing, imaging and condensing light. One type of OptiFocus™ lensed optical fiber includes monolithic devices that comprise a lens having a lens end portion attached to an end portion of a fiber. Some lensed fibers include a neck portion surrounding and end portion of the fiber, and the diameter of the neck portion of the lens is greater than the diameter of the fiber.
Examples of specific types of lensed fibers include, but are not limited to, collimating lensed fibers, focusing lensed fibers and tapered lensed fibers. Collimating lensed fibers are up to four times smaller than typical fiber-lens devices, and lensed fibers do not require any alignment of the lens to the fiber. Focusing lensed fibers are capable of focusing light beam sizes down to about six microns, with long working distances. Tapered lensed fibers include a high precision, tapered lens for high numerical aperture applications with short working distances.
To take advantage of the desirable performance characteristics of lensed optical fibers, methods and apparatus are needed to precisely align lensed optical fibers to form an array. One available technology is silicon V-grooves, which are used as fiber positioning elements. V-grooves are formed in a pair of upper and lower silicon substrates and fibers are placed in these grooves. The upper and lower substrates sandwich the fibers and hold the fibers in the grooves. However, V-groove devices have several limitations. For example, once a V-groove is fabricated, it serves to position the optical fiber only relative to the silicon substrate. The end of the fiber, which includes the lens, must still be positioned relative to other optical elements in the system. Such positioning is usually accomplished by micromanipulation and use of adhesives after micropositioning, which is expensive and time-consuming, especially in a mass production manufacturing environment. Another limitation of V-grooves for positioning lensed fibers is that the V-groove is sized to hold the fiber, but the V-groove is too small to hold the lens portion of the lensed fiber. An alignment method and apparatus is needed to hold both the fiber portion and the lens portion of the lensed fiber in position.
It would be desirable to provide alignment methods and apparatus for lensed optical fibers capable of aligning both the fiber portion of the lensed optical fiber and the lens portion of the fiber. Furthermore, there is a need to provide alignment methods and apparatus that do not require adhesives or thermal heat treatments and do not require complex manufacturing steps or elaborate micromanipulation to achieve alignment of the lensed optical fibers. Such alignment methods and articles would facilitate the manufacture of a wide variety of optical devices.